Primitive Archer
Main Discussion Area => Bows => Topic started by: Badger on July 03, 2007, 02:03:21 pm
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Any one ever notice set is not always the same even if it measures the same. I have noticed some bows will take some set and I give them a little shove backward and the set will appear to go away, as far as a photo goes anyway, other bows might take an inch or so of set and if you push back on it nothing happens, this bow is harder and will have higher brace height tension. I think on some wood the back will tend to pull the bow back into shape even though the belly has accumalaterd condierable stress damage allready. These bows will kind of have that rubbery feelingwhen not braced. Any other takes on this? Steve
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I made one like that, seemed like after about twenty inches, it didn't gain hardly any weight between there and 26". Shot like a bow ten pounds lighter.
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not enought experiance here to contribute ;D
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I'd say that the more the set is distributed over the entire limb, the faster it will recover. Sometimes its hard to see exactly where the set is coming from, I should do the limb drawings that Torges advocates. That'd give you a good look at just where the changes are occurring.
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Lennie, not so much about where the changes are occuring more in how they are occuring. Some bows can be hard as a rock with 1 1/2" set, others can be rubbery most are somewhere inbetween. My obeservation is that when you unstring the bow and push back on it, opposite the way you would push to brace you will notice that some bows just push right back into shape, other bows feel had and stay put right where they are while others most commonly will respond to a very firm push back to get a small response. I think moisture plays a good part in this along with some wood specimens just being better. Steve
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Maybe you guys can help me. I just finished tillering a red elm flatbow, 65" nock to nock, 1.75" wide at the fades, tapering about 16" from the tips to about 3/4" at the tips. The stave originally had about 2" of (deflex or reflex , always get those mixed up - the tips curved up in the direction of the back) on one limb, and a bit more on the other. The set was introduced during the first low brace tillering, not sure quite why, but it performs great. It is fast, very responsive, no hand shock at all, and just a lot of fun. It is far more accurate than I am, as well, and the sting is not exactly in the center of the handle, but that doesn't seem to affect it. The set is about 1.5" measured from the handle. It doesn't seem to lesson after unbracing it at all, for ten minutes of for two hours of shooting.
I like this bow, but wonder if maybe it is a failure? It pulls 50 lbs. exactly at 26.5".
Dane
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No, Dane, your bow is not a failure. If it were you wouldn't be enjoying it so. Badger, I think the last part of one of your posts hit it. Moisture may play a role in the phenomenon you describe. I really haven't noticed much difference in set except I always seem to get some. :) Jawge
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Jawge, thanks. I just got off the phone with Jamie, and he mentioned that the wood may have not been totally seasoned. Foolishly, I never checked with my moisture meter.
I'm going to let that process finish, and then finish and enjoy the bow.
Dane
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I know what you mean Steve and I agree.
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Yeah, I think I know what you mean. It's almost like the belly compresses and becomes stronger. Interesting.
J. D.
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I guess if your bow is more overbuilt then the belly wouldn't be as compressed and therefore might feel a bit spongier. I think heat treatment might also make for a harder, less spongy belly.
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Dane, your bow is not at all a failure, 1 1/2" set for a bow is pretty typical. I finished up a little elm bow last weeK that took almost 2" of set and when you brace the bow it feels like a bow with a little reflex, still very hard, bow shoots great, the osage bow I poste last week i think has a couple inches of reflex but is soft and does not perform well at all. I think my point is that you cant tell much just by looking at a bow. Last year I built a 140# osage longbow, I can easily brace the bow by myself and the bow took almost zero set, right now I am working on a 120# american longbow and I cannot brace the bow without help and it has about 1" of set. I can only bend it far enough for about a 3 1/2" brace height and my girlfriend has to slip the string on the nock for me while I hold it LOL. I think how carefully we work the bow down and not bracing it too soon have a lot to do with how hard the bow stays and how it will perform. Steve
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I better stop bracing my bows when they are still 90# + ::) ::) ::) ::)
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Dane, your bow is not at all a failure, 1 1/2" set for a bow is pretty typical. I finished up a little elm bow last weeK that took almost 2" of set and when you brace the bow it feels like a bow with a little reflex, still very hard, bow shoots great, the osage bow I poste last week i think has a couple inches of reflex but is soft and does not perform well at all. I think my point is that you cant tell much just by looking at a bow. Last year I built a 140# osage longbow, I can easily brace the bow by myself and the bow took almost zero set, right now I am working on a 120# american longbow and I cannot brace the bow without help and it has about 1" of set. I can only bend it far enough for about a 3 1/2" brace height and my girlfriend has to slip the string on the nock for me while I hold it LOL. I think how carefully we work the bow down and not bracing it too soon have a lot to do with how hard the bow stays and how it will perform. Steve
Steve, thanks. Here are a few shots of the bow as it now is.
[attachment deleted by admin]
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Dane,
The width profile of your bow in integral to it's analysis and hard to judge with just figures. While no project is a failure, every project offers an opportunity to imrpove the next one. Without seeing the width profile of you bow, I'd say you could have saved youself 1/2" or more of follow from having the limbs bend more evenly along it's limbs, towards the fades and/or mid limb to preserve this nice shooting manners, I would guess. I love elm for bow wood.
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I wonder if it's just different degrees of set, or if it literally manifests itself differently physically. I have this theory, I think I stole if from Lennie although I won't have to admit it if he doesn't remember, that wood can compress and have permanent distortion without having crushed otherwise work capable wood cells. I reckon the soft rings in ring porous (or even diffous porous) can be compressed leaving the summer rings undamaged. As their ability to withstand compression is weaker, they will fail "first." I reckon differences in species and specimen, the distribution of rings etc. could manifest itself in a good bit of variability in results with our projects.
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Where in the tree you get your stave from is probably the biggest factor as to whether or not your bow will have excessive set.This is if the wood is handled properly and the bow is built right. Your bow is, as Steve said, okay! I bet it is a smooth shooter.
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Dane,
The width profile of your bow in integral to it's analysis and hard to judge with just figures. While no project is a failure, every project offers an opportunity to imrpove the next one. Without seeing the width profile of you bow, I'd say you could have saved youself 1/2" or more of follow from having the limbs bend more evenly along it's limbs, towards the fades and/or mid limb to preserve this nice shooting manners, I would guess. I love elm for bow wood.
Getting the limbs to bend more toward the handle is one of the biggest challanges for me personnally, and I would have liked to have done that this time. However, I want to keep it at 50#, and not shorten the limbs (66"), so I will probably call it done and finish it. No hint of stacking, and it shoots sweet and fast. Next bow, I'll do better.
I love elm as well. It works so well for me. I have another elm stave waiting to be worked on, and am thinking of tackling a Holmgaard (sp?). Gods help me, :)
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Where in the tree you get your stave from is probably the biggest factor as to whether or not your bow will have excessive set.This is if the wood is handled properly and the bow is built right. Your bow is, as Steve said, okay! I bet it is a smooth shooter.
Thanks Matt. That is appreciated. And I don't know where in the tree the stave came from. I got this stave at the New England primitive meet last month. I'm writing an article on the event, so that will be forthcoming, if PA chooses to run it.
I have something really special planned for the finish on this bow, and I'm going to make a linen string for her, as well.
Dane
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Steve,
We usually look at set as the wood breaking down it compression. There may be more to it than this. Have we ever explored the break down of wood in tension? I believe that we assume that if the wood breaks down at all in tension that
the bow will come apart. I am not sure this is true. Also, set taken from wood being too wet seems to be different than wood that takes a set from exceeding its limitations.
Dan
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Dan, that was exactly the answer I was looking for, I have suspected tension breakdown for a long time as being a reason for different behavior in similar looking bows. I have some bows that I can saw up, Splitting the limb down the middle might make this pretty easy to check. I don't always do the best job phrasing a question as I did here, the type of set or behavior of the rested bow, rather than the amount of set is what the question here is actually about. Steve
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Dan and Steve, that's good stuff. We were always taught that there's the belly and the back and the line of separation between the two is the neutral plane. At least that's what the engineers taught us. I wonder if there is more interaction between the 2 than supposed. I don't know if a bow's back can cause set bit it can certainly cause breakage quicker. Jawge
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Jawge, you work with black locut a lot, and I know you haven't had much problem with it chrysaling, Does it tend to take less set than other woods i general or would you say about the same? Steve
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Badger, I would say it takes about the same set as other woods. Jawge
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This is an interesting discussion. I know exactly what you are talking about Steve. I have had bows that took set but were still firm and springy. You could bend them in either direction, but they would return to the same profile. Then you have another that takes set and acts like lead. You can bend it toward the back and it stays, you can bend it toward the belly and it stays. It seems like the bow is dead. Justin
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Dan there might be a little "tension set" in a bow, but typically I think the majority of set is compression set. Most woods have a much higher strength in tension, so typically you are operating well within the elastic limit. Moreso than the compression side.
I envision normal set, as compressing the spring growth near the belly surface until it has a density similar to the surrounding summer growth. That is why you see some set in most bows, and more set in a bow made from wood that has more spring growth. You still get some set in backed bows using quarter-sawn wood, so there is certainly an element of set that works on the summer growth exclusively. I've had better luck with quartersawn belly slats though, and I think the reason is there is summer growth throughout the full width. The trick with summer wood, is to adjust the limb width so you aren't "counting" the amount of spring growth.
It'd be simple enough to put some set in a slat, and then cut it in half and see which part shows the set. I've heard of people doing this, but haven't done it myself. Mostly I've heard that the set shows on the belly side almost exclusively.
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Lennie, I think you are missing the point of the post, nothing to do with how much set a bow takes but the kind of set a bow takes, there are worlds of difference in how bows take set even though they measure the same. Steve
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Steve, what about damage to the early growth rings throughout the bow, back to belly. I have had some hickory with early rings that were thicker and of lower density than usual. I bent one farther than I should have, and you could see the slippage between the solid, late growth rings. Not enough to delaminate, but enough to make feel like a laminated bow with wet glue. Not a colapse or crushing of cells in the summer growth, but a fracture in the cells of the early growth so they quit working. Still provided hysteresis and added mass though. Justin
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I find that woods such as Maple and HHB follow the string 'powerfully' meaning that they take that solid set that Steve describes. My theory is that the wood cells in these dense woods is very uniformly compressed and becomes denser as a result. Similar to a forgewood cedar shaft.
I think this effect is even more pronounced in wood that is pressed into service before it was fully seasoned. Several of the bows I made in my early bowyering days were from quick dried HHB. Even those which took excessive set were very good performers when the wood fully dried. I think the wood is more prone to developing this optimum type of set when stressed in an optimal moisture content for this to happen. Perhaps 15-20%.
I also tend to think that wood staying permanently stretched in tension is also a factor in inducing set. I once made a HHB bow that was finished and had zero set. There were some spots on the upper limb that had small patches of cambium remaining so I wiped the back with a moist towel and warm water and scraped it with a spoon tip. The bow was strung at the time and when I unstrung it the upper limb had developed a small amount of set. There is no way the moisture had penetrated the whole limb in the few minutes that took.
Pat
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Pat, I have experienced the same thing with both of those woods, too of my favorites. Elm is also one of my favorites but i have gotten that spongy set with more than one elm bow. Osage i have seen it several times.
Justin, you may have somethign there. I will start to try and be more concious of the process. I have had lots of problems with hickory, I seldom get the performance I want. I have always attributed this to moisture. Steve
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Steve I think I did address the "kind of set" issue. An overbuilt bow will have a different kind of set because its wood isn't compressed to the point where it is uniform. I think it would be the "spongier" kind of set you are talking about. A bow that has experienced near-maximal compression, would be hardened to its max and probably wouldn't be spongy or return sa quickly or as fast. Or is this still not pertaining to your discussion?
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Lennie, yest thats what I was talking about. I think the overworked underbuilt bow gets spongier than the overbuilt bow in most cases. However, I have experienced what you are talking about with hickory. Very often I am not able to get hickory to conform to my own mass theory. Most of the time it is because of moisture levels which for most woods would be acceptable. In these cases the bow is wider than should be needed but as you are saying on the spongy side, nothing extreme but not that good hard crisp feeling we have all come to know and love. Steve
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Steve,
Hickory is tricky. It likes to be drier than other woods. I had a longbow that I left in the house with the swamp cooler running all summer, then entered it in competition. This bow had already set several records. I had narrowed it and entered it in the 35# class.
It was a dead stick. I have it in my hot and dry shop now. I want to shoot it again at the end of the summer and see what it does.
It was Perry Reflexed, so it didn't show the set you would see normally, but it went spongy. Also, with hickory, I don't but it unless it is dense, resonous wood. The growth rings are mere dotted lines.
The 50# self bow broad head record you broke was set by Dewayne Smith with a Maple long bow I built, 72" long with 2 to 2 1/2 inches of set. It shot the broad head 202 yards. (He out shot me with my own bow! LOL It happens all the time)
What Lennie says about the compression taking most of the set is true. My point is Not that huge amounts of set are taking place in tension, but that there may be some set taking place here that we haven't looked for. You start to suspect the elasticity of woods when you build a lot of backed bows. You use the E- mod. of woods to compliment each other, but elastic modules is how hard a wood is to stretch. It has nothing to do with how elastic it is. I believe that some woods may stretch past the point of being able to return, and still be elastic enough to hold together.
As far as spring growth goes, I don't like woods that have a huge difference between the strength of the spring growth and hard growth. I hate it when a bow drops 15# of draw weight when broken in. It can be quite a guessing game.
Steve you wanted to identify different kinds of set. Here are 4 different kinds of set. Tension, moisture, Early growth break down
between growth rings, and compression set. It seems that your real question is, Does the set "always" compromise the fibers, and their ability to return to their shape when strained. You have already answered that question. This all comes back to what we talked about on another thread. We walk all around the real issue of how bows really work and why the mass theory model works as well as it does, without standing directly on the issue. I am working on this for my book, but their is some key info that I need before it is ready.
Dan
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Steve, I think you could adjust your mass theory for hickory. Weigh a piece at 9% MC like any other bow would like. Dry it out to 6% and weigh it again. Now subtract the difference from the weight in your mass formula. After you have an idea what the weight will be, you could just subtract it from all hickory bows.
Lets say you have a bow you want to end up at 21oz. You weigh it at 9% and it is 25oz. You weigh it again at 6% and it is 21oz. You just subtract that 4oz from the final. 21oz-4oz=17oz You want to tiller the drier bow to weigh 17oz. Justin
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Justin,
This is a good idea. It helps. The affects of moisture are more complicated though. IF it was just mass it would be easier. Draw weight and performance changes so much with the moisture. More than just the weight of it.
Dan
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Justin, pretty much as Dan said, the entire formula is performanced based and derived. Moisture control is one of the key elements even though some woods tolerate slightly higher or lower mc's than others. I have often felt that the best way to build a bow would be to overbuild it to start, make the best bow you can for the demensions you choose ignoring the draw weight. When you get all finished with your bow then just narrow the sides to attain the draw weight without affecting performance. I have done this many times with hickory that has a little higher than desirable moisture and it never fails they just come in far too heavy. Elm seems to hold on to moisture quite a bit also. Steve
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Steve,
I know exactly what you speak of, it mostly happens with my backed bows but also occurs with my selfbows. If I put in 6" of reflex in a boo bow and it looses half of that I can still bend it the opposite direction and it gains about 2" of reflex. I always worried that it could be a bad glue line until I tried it with a mulberry bow which had 11/2" of reflex and now has 1" of set. I wonder if its just the back of the bow trying to shrink and pull the bow into reflex and by bending it you are just speeding up the process??? Good topic !
-Alex
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Badger
I just read your recent comment in Beadmans thread....Inducing deflex/All reflexing
http://www.primitivearcher.com/smf/index.php/topic,57828.0.html
A bow that maybe only recovers 1/2" or so after shooting is better than a bow that recovers a full inch. If you loose 3" of that reflex and when you unbrace after shooting and it stays about the same you are good to go. The wood is still solid. Not all set is the same.
Question: do you make any conclusions from the speed of recovery, in addition to measuring the amount recovery?
Do you think that a bow that recovers less could have something to do with the four different types of set described in post 32 above?
thanks
willie
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I didn't read my original post because I know my views have changed quite a bit since I posted that. Intuitively I would sy the faster it recovers the better but anything that doesn't recover before the arrow leaves the bow is set. The only accurate way to check is really not worth the effort it takes, you need to shoot the bow through a shooting machine for an accurate speed reading and then take an accurate force draw curve to figure up your efficiency. String tension right after the shot is a good indicator. Or simply brace the bow and weigh it at full draw then let it up and weigh it at full draw again. They should be the same or as close as possible.
A couple of years ago I did a little study on how hysterisis is affected by set. I came to the conclusion that almost all the hysterisis is a product of set, even minor set which is unavoidable. If you were to test a bow at about 22" before it had taken even a whisper of set it will show very low hysterisis. This indicates that some of the recovery actually takes place durring the shot but not fast enough to deliver the energy to the arrow.
I kind of stumbled on to a method of tracking the hysterisis. A fiberglass bow has almost no hysterisis. If you calculate the virtual mass of a fiberglass bow it is very predictable with almost any arrow weight. A wood bow shows higher virtual mass as the arrows get lighter which means it is not recovering fast enough to keep up with the arrow. The more consistent a bows virtual mass across a wide range of arrow weight indicates how low of hysterisis a bow has. But honestly it is such a pain to do the test that just knowing the theory behind it is really good enough.
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I did'nt join this PA till 2011 but through investigation could of looked this discussion up.I'm probably missing some point here but as far as I'm concerned a mushy type limb pushed either way after unbracing has lost it.A noodle.No strength.When push pull unbracing a bow a person can feel how stout a bow is if it has a little reflex on it.It's a little hard for my mind to get around all that was discussed.
Checking a bows stress level with a digital poundage tester pulling to full draw/release slowly and then to full draw again is a good way to test and I do that at least and pay attention to that.Extended periods of bracing causes the same thing to happen.A little slower but still.
Seems like most bows I make are'nt broke in properly till at least 200 arrows go through it and at least 3 to 4 hours of bracing time at one time is done a few times on them.Then the bows show what they show and pretty much stay with that profile for the rest of their life.Broke in.Until someone really overdraws it good and then it's really broke in......lol.
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Thanks Steve,
I am still trying to get used to the Idea you are suggesting, and if I understand you correctly,....
a small amount of recovery (in spite of larger total set taken)
is preferable to a larger amount of recovery, even if the bow doesn"t retain much set from where you started?
I keep a "short as possible" longstring on my bow during the early stage of tillering, and can sometimes see recovery by watching the string "return", (right after the pull), that would be hard to see by measuring at the limbs.
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Ed
I like Steve's idea of watching string tension/early draw weight.
I wonder if anyone has seen or used a small digital inline scale that could be placed "in" the string ?
willie
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Well when a bow is on a short as possible long string a person can see the amount of poundage it takes to get the tips 6" past the handle after it's tillered would'nt you think?
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sorry for the confusion, Ed. My fingers and keyboard cannot keep up with the flow of ideas sometimes.
I was thinking more about after the bow has been braced with a normal string. Perhaps it might be more telling to watch a scale in the string, immediately after pulling. than to detect a weight loss on successive pulls.
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Badger, I have a firm beliefe that there is no better bow wood than elm. I just wish I knew for certain the species of elm it is that does so well.
I have built one red elm bow before. It was 2 inches wide, 68 long and 40@28. It was so spongy i could push down on the upper limb and it would spring to brace. I could throw an arrow faster than it could shoot. I had a very similar experience with black locust before too. No ammount of heat treat would get these bows to perform. I noticed something both these bows have in common, and something in common with my least performing osage. Ring count.
The ring count on the locust and elm were very low. Both bows had only two rings, with the early wood placed dead center of the limb. All my slowest osage bows have thick rings. All my fastest have higher ring count. Perhaps that can contribute.
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willie....That would be hard to do in the string like that,but there's all kinds of innovative crafty people on here so I can't say it can't be done.....lol.Just not by me yet anyway.
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Sleek
in post 32 above, Dan identifies four different causes that could induce set. One that he mentions is "Early growth break down between growth rings". Having that single early ring in the center of the limb may bring out the type of failure he mentions. This is often described as a failure in "shear" by engineers, and not uncommon in certain beam configurations.
My interest in this inquiry, is that it would be nice to be able to learn how to identify the different types of set as they rear their ugly heads while tillering. Perhaps letting us know whether the stave needs heat treating, a better back, just more time drying, or an early retirement.